Network operators and carriers are deploying packet-switched communications networks in place of circuit-switched networks. In packet-switched networks such as Internet Protocol (IP) networks, IP packets are routed according to routing state stored at each IP router in the network. Similarly, in Ethernet networks, Ethernet frames are forwarded according to forwarding state stored at each Ethernet switch in the network. The present invention applies to communications networks employing any Protocol Data Unit (PDU) based network and in this document, the terms “packet” and “packet-switched network”, “routing”, “frame” and “frame-based network”, “forwarding” and cognate terms are intended to cover any PDUs, communications networks using PDUs and the selective transmission of PDUs from network node to network node.
Multicast forwarding of data packets (where packets are sent from a source node to multiple destination nodes more or less simultaneously) is of increasing importance as demand for services such as PTV and Video on Demand (VoD) grows.
In Ethernet networks, Provider Backbone Transport (PBT), also known as Provider Back-Bone Bridging-Traffic Engineering (PBB-TE), as described in Applicant's British patent number GB 2422508 is used to provide a unicast Ethernet transport technology. Provider Link State Bridging (PLSB) as described in Applicant's co-pending U.S. patent application Ser. No. 11/537,775 can be used to provide a multicast transport capability for Ethernet networks using IS-IS to set up unicast paths and multicast trees in the network. Both above patent documents are hereby incorporated by reference.
Provider Link State Bridging (PLSB) typically uses protocols such as Intermediate System-Intermediate System (IS-IS) or Open Shortest Path First (OSPF) to exchange topology, addressing and service information to enable the calculation of paths for forwarding packets from any given source node to one or more destination nodes, and to install the forwarding state required to implement those paths. OSPF and IS-IS are run in a distributed manner across nodes of the network so that each node will locally compute paths based on the view of network topology shared by the routing system.
As is known in the art, IS-IS and OSPF are “routing” protocols, in which “Dijkstra” or similar algorithms are used to compute shortest paths between any two nodes in the network. Once computed, these shortest paths can then be used to derive unicast paths and multicast trees, and to determine the forwarding state that must be installed in each node in order to implemented the derived paths and trees. Techniques such as Reverse Path Forwarding Check (RPFC) can be used to mitigate the effect of any loops that may form transiently during periods when multiple distributed peer nodes independently compute paths and install the forwarding state.
An advantage of the above described system is that the same algorithms can be used both at the time that a new service instance is requested, and to recover from a network failure. For example, when a client requests the provisioning of a multicast tree between a given source node and a set of destination nodes, information shared via IS-IS can be used by each node to compute the multicast tree, and install the appropriate forwarding state in each node traversed by that tree. If a topology change occurs in the network, such as a node or link failure, this information will be flooded to all nodes by the protocol's operation, and each node will locally recompute paths as required based on a consistent view of the changed network topology.
While this approach provides a flexible method for recovering from network failures, it suffers a disadvantage in that there is no easy way to implement traffic engineering in a network that is operating properly (i.e. in the absence of a network failure). It computes paths on the basis of available capacity, not offered load. Optimization of paths on the basis of offered load is a substantially more computationally intensive problem typically requiring offline planning tools.
Techniques for managing traffic flows, especially multicast traffic flows, in a packet network which overcome at least some of the above-noted issues remain highly desirable.